The present invention relates to a scroll type compressor and, more particularly to an arrangement for reducing a load upon starting of the scroll.
In a conventional scroll compressor, an orbiting scroll generally comprises an end plate and a spiral wrap located on the end plate in upstanding posture, with a rear side of the end plate having a bearing for orbital motion and a self-rotation preventing mechanism for the orbiting scroll. A fixed scroll also includes an end plate and a spiral wrap located thereon in upstanding position in the same way as the orbiting scroll, with the fixed scroll having a suction port and a discharge port formed in the outer periphery and the center portion of the end plate, respectively.
The orbiting scroll and the fixed scroll are assembled together with their wraps facing inwardly and held in interposed relationship between the fixed scroll and a frame of the compressor.
In the scroll compressor described above, when the orbiting scroll executes an orbital movement or revolution without the rotation about its own axis, the spaces defined by the end plates and the wraps of the orbiting and fixed scrolls are gradually reduced in their capacities as they move toward the center of the scrolls, so as to compress gas which has been drawn in from the suction port and deliver the compressed gas through the discharge port. That is, the gas confined within the spaces at the outer periphery of the wraps is progressively compressed, as the spaces move toward the center of the scrolls, to a constant capacity ratio. In the case of an usual compressor for an air conditioner, the capacity ratio is set about 2.5 to 4. Thus, the suctioned gas is compressed until it attains a predetermined pressure level. Also, in the compressor for an air conditioner, an inlet pressure and an outlet pressure are balanced during the period of stopping operation, with balanced pressure being two or three times as high as the usual suction pressure.
However, when the compressor is restarted, because it compresses the gas of the balanced pressure to its capacity ratio, the pressure in the compressed spaces is two or three times higher as compared with the pressure in an ordinary operation. Therefore, the starting load becomes large and sometimes it becomes almost impossible to start operation of the compressor. In, for example, U.S. Pat. No. 4,389,171 a method for reducing a load upon starting a compressor is proposed.